The present invention relates to a cigarette manufacturing machine.
Cigarette manufacturing machines are known to employ a distributor for receiving shredded tobacco from a feeder and supplying it, via a carding unit and drop-down duct, towards a withdrawal unit which extracts the shredded tobacco from the bottom end of the said drop-down duct and feeds it, in the form of a relatively thin layer, on to a conveyor belt. By means of the latter, the said layer of tobacco is fed into the bottom end of an upward duct into which the tobacco particles are usually sucked up and deposited on to one or more suction belts on a unit for producing a continuous cigarette rod.
The main requisite of a cigarette manufacturing machine is to ensure the continuous cigarette rod is as homogeneous as possible. Generally speaking, the homogeneous nature of the said cigarette rod depends on how homogeneously the tobacco layer is formed on the said conveyor belt which, in turn, depends on the regularity with which the said withdrawal unit extracts the tobacco from the bottom end of the drop-down duct and on the manner in which the tobacco is fed down the latter.
On known cigarette manufacturing machines, the said drop-down duct is usually of constant section, essentially rectangular, with its longer side extending crosswise in relation to the travelling direction of the said conveyor belt.
Experiments have shown that a constant duct section prevents the mass of tobacco fed into the said duct from being blended or its density from being varied as it falls down the duct. Consequently, the unhomogeneous nature of the original mass of tobacco invariably influences the quality of the tobacco layer formed on the said conveyor belt. Furthermore, for a given shape of the drop-down duct section, the density of the tobacco fed into the duct tends to vary, not only from one section to another, but even within each section, such variation being proportional to the ratio between the lengths of the longer and shorter sides of the said section.